The present invention generally relates to Multiple-Input Multiple-Output (MIMO) based wireless communication receivers, and particularly relates to correcting data transmission errors by MIMO-based wireless communication receivers.
The acronym ‘MIMO’ refers to a broad spectrum of wireless communication technologies that incorporate multiple transmit and receive antennas for improving data transmission performance. Particularly, MIMO-based wireless communication systems improve spectral efficiency by combining temporal processing with spatial processing, thus exploiting the spatial dimension of a wireless communication channel. For example, MIMO-based wireless communication systems may improve data transmission rates by employing a spatial multiplexing technique. In addition, the adverse effects associated with channel fading may be reduced by employing space-time diversity coding schemes.
Wireless communication systems having a rich multi-path fading channel environment may incorporate multiple transmit and receive antennas for improving system performance. For example, cellular-based systems using Wideband Code Division Multiple Access (WCDMA) technology may utilize multiple transmit and receive antennas. Likewise, Wireless Local Area Networks (WLAN) using the Orthogonal Frequency Division Multiplexing (OFDM) access technology may also utilize multiple transmit and receive antennas. On the transmit side of a conventional MIMO-based system, turbo encoded data is interleaved and de-multiplexed into distinct streams of data, where each data stream corresponds to a particular spreading code and transmit antenna combination. The spreading codes may be re-used across transmit antennas, and each transmit antenna may send a unique pilot code to assist receiver synchronization and channel estimation. On the receive side, transmitted data streams arrive superimposed at each receive antenna. As such, a composite signal received by a plurality of receive antennas may comprise various delay and/or phase shifted instances of the same data streams, e.g., various instances of the same WCDMA or OFDM symbol streams.
Although MIMO-based wireless communication systems may improve system performance as compared to single-antenna systems, they still experience data transmission errors due to channel-induced noise and interference. Interference may arise in a MIMO-based system due to simultaneously transmitted streams of data interfering with each other. For example, in an OFDM-based system, simultaneously transmitted streams of data may use the same frequency tone, also referred to as sub-carrier frequency. Alternatively, in a WCDMA-based system, simultaneously transmitted streams of data may use the same channelization codes.
A conventional scheme for correcting data transmission errors in MIMO-based systems is HARQ—Hybrid Automatic Repeat Request. HARQ exploits the high coding gain associated with Forward Error Correction (FEC) and the rate flexibility associated with the Automatic Repeat Request (ARQ) protocol. HARQ utilizes physical layer acknowledgement signaling between transmitters and receivers to facilitate re-transmission of erroneously received data. In addition, re-transmitted data may be combined with previously received data, thus improving data decoding reliability.
Two predominant conventional HARQ-based combining schemes are Chase combining and Incremental Redundancy (IR). Chase combining is a reduced-complexity technique whereby each erroneously received data packet or stream is re-transmitted. On the receive side, the re-transmitted data is combined with the corresponding previously received data. Alternatively, the IR combining technique does not retransmit entire coded data packets or streams. Instead, a wireless transmitter incrementally sends additional redundant information, e.g., parity bit, to a corresponding receiver if data decoding fails. The receiver then uses the redundant information to improve decoding of the erroneously decoded data. Regardless of the particular combining scheme, conventional HARQ-based error correction techniques utilize the retransmission of data to correct data transmission errors.